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Old 10-05-2020, 18:46   #1
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Yanmar 4JH3TE Overheating

Hello all,

I need some advice. I have a 4JH3TE that I cannot get over 50% RPM without overheating, or at least almost getting to 230 degrees. When at idle it's fine or even 1300-1500 RPM. Anything over that the engine gets extremely warm.

I can sit at the dock and run WOT to 3800, no problems. But when under load it overheats.

I have changed the coolant, thermostat, cleaned the heat exchangers, and checked all hoses for circulation.

I will also say I have a fixed prop that is about 4" from the hull and has 600 hours on it.

I have been having this problem for 7 years and am tired of throwing money at it.

Can any of you smarter than me give some suggestions?

Thanks...
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Old 10-05-2020, 23:38   #2
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Re: Yanmar 4JH3TE Overheating

Welcome aboard CF, Sammyb.

Have you confirmed your temperature sensor and gauge is reading correctly. Put another way, have you confirmed the engine is actually overheating by using another temperature measuring device?
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Old 10-05-2020, 23:46   #3
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Re: Yanmar 4JH3TE Overheating

Have you checked your mixing elbow? Also could it be an issue with one of the water pumps / impeller?

What is water flow like out of the exhaust pipe?
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Old 11-05-2020, 07:23   #4
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Re: Yanmar 4JH3TE Overheating

The water flow is fine, Changed the impeller, and used several temp guns.
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Old 11-05-2020, 07:26   #5
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Re: Yanmar 4JH3TE Overheating

Assuming running gear and bottom are clean. Can you get close to 3800 rpm under way? If not, you have the wrong prop.

How many hours on the engine and exhaust elbow?
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Old 11-05-2020, 07:35   #6
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Re: Yanmar 4JH3TE Overheating

Yes the bottom and prop are cleaned regularly, I have about 650 hours on her. All heat exchangers have been cleaned.
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Old 11-05-2020, 07:49   #7
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Re: Yanmar 4JH3TE Overheating

But did you open and check mixing elbow? On my last yanmar which had a different (and inferior imo) elbow design, I had similar issues with water flow fine. However when I checked the part.. the exhaust side was 80% blocked... water side was fine.
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Old 11-05-2020, 07:53   #8
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Re: Yanmar 4JH3TE Overheating

Interesting, I guess the mixing elbow is my next inspection. Did you just remove it and inspect it?
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Old 11-05-2020, 07:56   #9
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Re: Yanmar 4JH3TE Overheating

Yes.... took the hose off and then removed from engine. Again, on my old engine 3HM35F, the elbow was a different design but same principle. I wonder if you could start with removing just the hose and taking a look......

Good luck
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Old 11-05-2020, 17:46   #10
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Re: Yanmar 4JH3TE Overheating

Lots of things to try. We have a similar engine, and had similar, but not as bad, problems you did. On top of what you've done:


As others have said, check your elbow, they are a maintenance item.


I think yours is turbocharged, right? Make sure the turbo is clean and spinning freely. You can check it when you pull the exhaust elbow. If the turbo does not spin VERY freely (like for several seconds by flipping it with your finger), pull it and have it rebuilt.



Check your thermostat? Actually, just change it.


Check your coolant mix. 50-50 MAX. If you are where it's warm, you can go down to about 30-35%. Coolant does not exchange heat as well as water. This is a VERY common problem. A tester is less than $10 at the autoparts store.
Add "Wetter Water" to your coolant. This was a HUGE difference maker for us. It really helps heat exchange.



As others have said, make sure your prop is 1) clean 2) spins freely/doesn't bind and 3) isn't overpropped. This happens ALL of the time.
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Old 11-05-2020, 19:22   #11
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Re: Yanmar 4JH3TE Overheating

Quote:
Originally Posted by Sammyb View Post
Hello all,

I need some advice. I have a 4JH3TE that I cannot get over 50% RPM without overheating, or at least almost getting to 230 degrees. When at idle it's fine or even 1300-1500 RPM. Anything over that the engine gets extremely warm.

I can sit at the dock and run WOT to 3800, no problems. But when under load it overheats.

I have changed the coolant, thermostat, cleaned the heat exchangers, and checked all hoses for circulation.

I will also say I have a fixed prop that is about 4" from the hull and has 600 hours on it.

I have been having this problem for 7 years and am tired of throwing money at it.

Can any of you smarter than me give some suggestions?

Thanks...


After 7 years of living with a slow overheat I suppose you must have tried just about everything so on the assumption that the raw water pump is working reasonably well, the thermostat is still in place and the mixer elbow isnít restricted here are a few ideas that might help cool er down.
The heat exchanger on your engine is a two pass type, seawater in and out at the same end and the flow is separated by the end plate ridge and and a gasket with a cross piece that seals the end plate ridge across the core. There are 2 main things that can go wrong here.
1. The gasket is missing at the cross piece.... no big deal but less raw water flows through the core and it does the shortcut to the mixer elbow.
2. The core is not in the correct position rotationally. This is way more important because the raw water flow through the tubes is compromised by the shape of the tube stack and the fresh coolant flow is also restricted by the outer sleeve cutout not being in alignment with the coolant port so actually 2 reasons for the engine temp to rise. There is a ⅛Ē diameter air bleed hole in the outer sleeve that needs to be on the top during installation.
Here,s a pic of the 4JH cooling system. I have a few old tubestacks and Iíll post a pic of one that shows what I mean better than words. Click image for larger version

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ID:	214874Click image for larger version

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Old 11-05-2020, 19:36   #12
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Re: Yanmar 4JH3TE Overheating

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